ABSTRACT- Members of the nicotinic acetylcholine receptor (AChR) gene family mediate synaptic transmission throughout the central and peripheral nervous systems. The AChR family is part of the superfamily of pentameric ligand-gated ion channels (pLGICs) that also includes receptors activated by the neurotransmitters serotonin, gamma-amino-butyric acid, and glycine. Collectively, the pLGIC superfamily mediates the majority of neurotransmission occurring on the millisecond time frame. The over-arching goal of our research is to understand mechanisms by which AChRs transduce a chemical stimulus into an electrical response, a process central to understanding disorders of excitability caused by inherited mutations of AChR, and to developing drugs to treat such disorders. Toward this end, the proposed studies address key gaps in our understanding of chemo-electrical transduction by the AChR spanning from basic to translational science. The first aim is to delineate biophysical and structural mechanisms by which ion transport through the AChR channel is coupled to gating of the channel between inactive and active states. The second aim is to elucidate biophysical and structural mechanisms by which changes in extracellular calcium, a major regulatory ion, modulate the strength of signaling by the major type of AChR in the brain. The third aim is to delineate mechanisms by which inherited mutations in the major type of brain AChR cause epilepsy, and develop mechanism-based therapeutic solutions. To achieve these aims, we employ a multidisciplinary approach that includes functional measurements from single AChR molecules, computational methods to simulate atomic scale interactions between AChRs and physiological modulators, and atomic-scale structure determination of normal and diseased AChRs. The overall studies will resolve key gaps in understanding AChR signaling mechanisms central to physiology, pharmacology, and pathophysiology. The insights will apply not only to AChRs from muscle and brain studied herein, but also to other members of the pLGIC superfamily.